The present invention concerns polyurethane backed carpets wherein the backing composition contains a thermoplastic polymer incorporated therein.
Synthetic based carpets backed with polyurethane generally have a tendency to undergo curling at their periphery when moisture or certain organic solvents are absorbed.
This edge curl phenomenon is believed to pertain directly to the back stitch loops of the carpet fibers that are firmly encapsulated with the polyurethane backing material. Certain carpet fibers, such as nylon, are highly sensitive to moisture and organic solvents, yet their back stitch loops are the high strength member of the system. The polypropylene primary backing, which is impervious to moisture, is the high tension member of the system. When the surface fibers and/or back stitch loops absorb moisture or organic solvents present in installation adhesives, the loops tend to swell or enlarge. Collectively, the enlarged loops create a bending moment that is perpendicular to the primary backing and subsequently the carpet curls at its periphery and in extreme cases, buckles. However, in accordance with the present invention, woven synthetic, particularly polypropylene, primary backed carpets are provided with an improvement in one or more of its properties such as tack-free time, edge curl performance or tuft lock by incorporating minor amounts of a thermoplastic polymer of one or more ethylenically unsaturated monomers into a urethane forming composition.